In optical communications, light measurements, and other fields, members for positioning and fixing the ends of optical fibers are needed to form optical connections among a plurality of optical fibers or between a plurality of optical fibers and other elements (for example, optical waveguides for the branching of optical communications signals). Methods for manufacturing such optical fiber fixing members by press molding with good productivity and reproducibility have been used in recent years.
For example, Japanese Unexamined Patent Application HEI8-292332 (hereinafter abbreviated as "the Application") describes a method in which a press mold for the transfer of grooves designed to fix the ends of optical fibers is manufactured by grinding, and glass is press-molded with the aid of this mold, yielding an optical fiber fixing member. According to the Application, the resulting optical fiber fixing member is advantageous in that peak chipping and damage to the optical fibers to be fixed can be prevented because the fixing member can be rounded off such that the peaks between the fixing grooves have a specific radius of curvature in cross section.
The mold for the press molding of optical fiber fixing members described in the Application is fabricated by grinding, and the ground surfaces of this mold inevitably contain numerous minute irregularities. Peaks between the V grooves for engaging and laying out optical fibers are transfer-formed by the bottom portions of concavities in the mold, and because the transfer surfaces of the bottom portions of the concavities in the mold are formed as described above, irregularities due to surface roughness result, as do irregularities in the form of clearly visible folds.
With press molding, microscopic shapes are transferred in addition to the macroscopic shape of the mold. In particular, the aforementioned microscopic shapes are transferred with high accuracy in molding operations in which the shape of the mold is transferred with very high accuracy, such as near the optical fiber supports of optical fiber fixing members. Release films are sometimes formed on the transfer surfaces of molds, but the minute irregularities on the mold surfaces are transferred by the molds even in the presence of such release films.
Molded surfaces of optical fiber fixing members are therefore almost identical in texture (surface hardness, fold-like irregularities resulting from machining, surface warping, and the like) to the surfaces of molds, and minute irregularities are also formed on the surfaces of peaks between the V grooves of a molded article.
When optical fibers are assembled into an optical fiber array by being aligned in the V grooves and fixed in place by mechanical means or by adhesion, the optical fibers are aligned in the V grooves by being pressed against the walls of the V grooves, but when minute irregularities such as those described above are present on the peaks between the V grooves (with which the optical fibers are most likely to come into contact, particularly during pressing), the lateral surfaces of the optical fibers are damaged, and microcracks form.
In view of this, the invention described in the Application entails rounding off the peaks of optical fiber fixing members in cross section, and is thus useful in preventing optical fibers from undergoing comparatively extensive chipping, notching, or the like. It is unavoidable, however, that numerous minute irregularities still remain, making it impossible to prevent microcracks such as those described above from forming. It is also indicated in the Application that the peaks are rounded off by polishing, but such polishing involves corner chamfering and is incapable of removing the numerous minute irregularities on the peak surfaces.
A resulting drawback is that when light is transmitted by such an optical fiber array, the propagating light is scattered at locations where microcracks are present, resulting in increased transmission loss. In addition, even cracks that are small enough not to have a direct effect on reduced transmission loss eventually develop into larger cracks as a result of thermal stress due to variations in ambient temperature, bringing about an increase in transmission loss. At the worst, optical fibers break and completely lose their ability to function as a light-transmitting medium.
Another drawback is that because a molded article and a mold adhere to each other in the vicinity of optical fiber engagement portions during the formation of fixing grooves, the molded article exhibits poor release properties when it is removed from the mold following press molding, and a high fill factor is achieved by the molding material (material being molded) in relation to the volume of the mold cavity, making it more likely that molding burrs will form.
In addition, conventional optical fiber fixing members are molded by completely covering the molding surfaces of the mold with a molding material during the molding of the peaks between the optical fiber engagement grooves, so these peaks are mold transfer surfaces. Such optical fiber fixing members develop compression strain (stress) during the molding of the entire molding area of the optical fiber engagement grooves. A resulting disadvantage is that cracks form near the optical fiber engagement grooves, particularly in the bottom portions of the optical fiber engagement grooves, where stress is apt to concentrate for structural reasons.
An object of the present invention is to overcome the above-described drawbacks of prior art and to provide an optical fiber fixing member whose purpose is to ensure better release properties, to improve burr control properties, and to prevent transmission loss from being increased by the microcracking of the optical fiber, as well as to provide a method for manufacturing this member, an optical fiber array constructed using the aforementioned optical fiber fixing member, and a method for manufacturing this array.